(a) Industrial Field of the Invention
The present invention relates to a method of orienting a liquid crystal optical device and to an apparatus usable for the method. Particularly, the present invention relates to a method of orienting a liquid crystal optical device which can be advantageously employed as a practical method of orienting a liquid crystal material in the production of a liquid crystal optical device whereby providing a liquid crystal optical device comprising a highly oriented smectic liquid crystal and being suitable as a liquid crystal display device, a liquid crystal memory device or the like. Further, the present invention relates to an apparatus which can be suitably used for the method of orienting a liquid crystal optical device.
(b) Description of the Related Art
In recent years, liquid crystal optical devices produced by employing a ferroelectric liquid crystal among smectic liquid crystals as a liquid crystal material, precisely controlling the orientation of the ferroelectric liquid crystal, and supporting the liquid crystal material between two substrates carrying their respective electrode layers have been attracting interest because of their excellent qualities, for example, high-speed response to external factors, such as an electric field, and high contrast ratio, and accordingly, their use for liquid crystal display devices, liquid crystal memory devices, etc. has extensively increased.
In order to attain such excellent qualities, it is necessary to control the orientation of the liquid crystal material, i.e. the ferroelectric liquid crystal, to a high degree, and therefore, there have been proposed various methods of controlling the orientation.
For example, when a low molecular weight ferroelectric liquid crystal is used as the ferroelectric liquid crystal, the orientation control has been conducted by using a rubbing technique, a shearing technique, a temperature gradient technique, a sio oblique evaporation technique or the like.
However, the orientation control using these techniques has deficiencies such as complicated pretreatment of substrates and complicated control operations. Further, the usual use of glass substrates causes problems such as difficulty in continuous production because of the troublesome conveyance process, difficulty in enlargement of area, etc.
In the conventional rubbing technique, the orientation of liquid crystal molecules is induced by an orientation layer, such as a polyimide or polyvinylalcohol, which has been oriented by a rubbing treatment after having been provided on the surface of a glass substrate for supporting liquid crystal, and in order to improve the conventional rubbing technique, there have been proposed some orientation control methods, for example,
(1) in Japanese Patent Application Laid-open No. 63-14,125, is disclosed a method of orientation in which a liquid crystal is oriented on a rotating drum previously provided on its surface with an orientation layer and then, the oriented liquid crystal is transferred on a substrate to produce a liquid crystal optical device;
(2) in Japanese Patent Application Laid-open No. 63-64,027, is disclosed a method of orientation in which while, in the conventional rubbing technique, the orientation of liquid crystal is induced by an orientation layer, such as a polyimide or polyvinylalcohol, oriented by a rubbing treatment using a flocked fabric which causes the generation of a large amount of dust and scores in the orientation layer and also creates difficulty in the production of very thin cells, the orientation of an orientation layer (a polyimide, etc.) is conducted by pressing or rubbing the layer using a material having a hardness equal to or harder than that of the orientation layer, to prevent the generation of dust and maintain the rubbed surface smooth; and
(3) in Japanese Patent Application Laid-open No. 63-66,534, is disclosed an orientation method wherein rubbing treatment is conducted during shifting the relative positions of the rubbing material and the substrate in a direction intersecting perpendicularly to the rubbing direction, to prolong the exchange cycle of the rubbing material and attain a uniform rubbing in a large area.
The above method (1), however, has problems in that
(a) in order to apply the liquid crystal uniformly on a drum, it is required to control the viscosity of the liquid crystal by properly adjusting the temperature of the liquid crystal;
(b) waiting time is required for cooling the liquid crystal because the liquid crystal should be oriented in the course from its application on the drum to its transfer to the substrate; and
(c) complicated optimization of every condition, for example, the kind of the polymer to be applied, the shape of the groove in the drum, and so on, is required because the orientation state of the liquid crystal widely varies depending on the conditions.
The above method (2) has problems in that
(a) there is required a production process no less complicated than the usual production process employing the usual rubbing technique;
(b) it is difficult to attain uniform orientation over a large area;
(c) when a flexible substrate, such as a plastic substrate, is used, there is a possibility of damage of the slender electrode caused by the deformation of the substrate during pressing; and
(d) in common with the usual rubbing technique, this method also needs steps of vacuum injection and slow cooling of liquid crystal, which make it difficult to reduce the producing time.
Further, the above method (3) also has problems in that
(a) the method requires such a complicated process that a high production cost is inevitable;
(b) very accurate table and rubbing roll are required for orientation in a large area; and
(c) the producing time is no shorter than the usual rubbing technique.
On the other hand, relating to the apparatus for orienting liquid crystal optical device to be used in the step of orienting liquid crystal material, various apparatuses have been proposed depending on orientation methods including those described above. As apparent from the problems described above, each of those apparatuses have deficiencies that continuous production is difficult, and that it is difficult to attain efficiently a high degree of orientation because of the necessity for a complicated components or construction, and so on.
In addition, the conventional methods of orienting liquid crystal optical devices and the conventional orientation apparatuses used therefor have serious problems in that realization of continuous operation is difficult in both cases of cut sheet type and lengthy panel type of liquid crystal optical devices, and that only low productivity is expected.